The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art.
An RSA-based cryptosystem, which is widespread in current communication systems, is to utilize a very difficult mathematical problem as a public key for encrypting data, and to use the solution thereof as a private key for decrypting the encrypted data, working based on mathematical complexity.
A cryptosystem based on mathematical complexity is considered to become fundamentally decipherable when a new prime factorization algorithm or a quantum computer is developed. As a counter-measure to solve such a security issue, a security method using a quantum cryptography is emerging.
Where a quantum key distribution is used, the act of tapping or eavesdropping on communications from a third party other than the transmitting and receiving parties changes the quantum state, and thus renders the original encrypted content indeterminable, and additionally uncovers the tapping attempt.
To normally operate a quantum key distribution system, an optical system needs synchronization and stabilization to counter errors due to external environmental changes. In other words, start-points of quantum data or a modulated quantum signal sequence need to be accurately synchronized between a transmitting apparatus and a receiving apparatus of the quantum key distribution system.